Side fire laser assemblies may be used for laser-based surgical procedures, for example, to deliver laser energy of a specific wavelength at a specific pulse rate to remove tissue through vaporization. Such procedures may be performed in an aqueous environment, for example, under water.
FIGS. 1 and 2 show a conventional side fire laser assembly 100 including a side fire optical fiber 130. An end 132 of the optical fiber 130 may be polished at a specific angle such that energy is emitted to a side of the optical fiber, as opposed to the end. To permit the laser to emit energy at the correct angle, an air interface is provided at the polished end 132 of the optical fiber 130. As shown in FIG. 1, an air gap 160 is formed in the conventional laser assembly 100 when a capillary tube 150 is fused to the optical fiber 130 and an end 152 of the capillary tube 150 is heated until the end of the capillary tube 150 collapses, thereby forming the air gap 160. As shown in FIG. 2, a metal cap 200 may be placed over the end 152 of the capillary tube 150. During a procedure, as noted below, up to 100 W (watts) of energy may pass through the optical fiber 130 at pulse rates up to 50 Hz (Hertz). This pulsed energy may create vapor bubbles upon exiting the optical fiber 130. These vapor bubbles may collapse back violently onto the face of the optical fiber 130. The metal cap 200 helps to reinforce the capillary tube 150 during energy delivery through the laser assembly 100.
When using this conventional laser assembly 100, a portion of the laser energy may leak from the distal end 132 of the optical fiber 130, thereby reducing the efficiency with which laser energy is delivered to the treatment area in the patient and/or overheating the metal cap 200 that is used to protect the optical fiber 130. For example, this conventional laser assembly can operate at 100 W of average power. This means that, for every second, 100 J (joules) of energy pass through the optical fiber. The laser assembly can operate in a pulse mode with a pulse rate of 50 Hz and a pulse duration of only 200 μs (microseconds). Each pulse therefore delivers 2 J (100 J/50 Hz) and 10,000 W of power (2 J/200 μs=2 J/0.2×10−3 s=10×103 W). The efficiency of energy transition between the optical fiber and the outside media in the conventional laser assembly may be 96-98%. This means that 2-4% of energy is lost by being converted to heat, creating about 200-400 W of heat for every pulse. Most of the loss by heat generation happens in a very small volume on the end of the capillary tube where the energy beam changes direction and transits from glass into water. If the heat is not dissipated efficiently, the temperature in the end of the optical fiber can rise higher than the structure can handle.
Accordingly, cooling of the device may be needed to operate the laser assembly at a safe temperature. In some instances, the overheating that can occur from laser energy leakage can affect the mechanical and/or optical properties of the end of the optical fiber, the capillary tube, and/or the metal cap. In other instances, the overheating that can occur from laser energy leakage can be sufficiently severe to damage the end of the optical fiber, the capillary tube, and/or the metal cap.
Besides high temperatures, intense vibrations may be generated during each laser pulse. These vibrations may cause glue that attaches the metal caps to the capillary tube to break away. As the glue dislodges, the capillary tube is allowed to vibrate more freely. The vibration of the capillary tube may be so intense that the glass of the capillary tube may begin to break or fracture.
Accordingly, a need exists for a laser assembly that can withstand high temperatures and/or vibrations.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention.